1. Field of the Invention
The present invention relates to an operating device.
2. Description of the Related Art
Conventionally, as an operating device including a switch member having a shaft member and an operating member having an engaging part with which the shaft member is engaged for mounting, there has been known a volume switch provided on an operating panel of an audio unit or the like for adjusting a level of sound volume, and so on.
In the above described operating device, specifically, the operating member is a knob which a user grips with his fingers or the like for rotational operation. The knob is mounted on the operating panel in a manner projected therefrom so that the rotational operation can be easily conducted.
By the way, in a case of mounting the above described operating device on an instrument panel of an automobile, in European area, following standards (1) and (2) are provided from a viewpoint of ensuring safety of passengers (especially children (infants)) in an event of a collision.
(1) A protruding amount of the operating member from a surface of the operating panel should be within a prescribed amount.
(2) In a case where the protruding amount of the operating member from the surface of the operating panel exceeds the prescribed amount, when a prescribed load is applied to the operating member in an axial direction, the operating member should be pushed down to the operating panel by this load so that the protruding amount of the operating member may be kept within the prescribed amount.
The prescribed load in the above described standard (2) is provided to prevent a child (an infant) from suffering injuries with a projected portion by a collision, and set to be about 378N (Newton), considering an impact load when a head of a child (infant) is struck.
The protruding amount of the operating member prescribed in the above standards (1) and (2) is specified to be the smallest necessary amount that the user can grip the operating member, in order to avoid an injury to the head of the child (the infant) caused by a contact of the head with a corner of the operating member, when the head is struck the operating panel.
Accordingly, in a case where the operating device is designed in compliance with the above described standard (1), a gripping allowance of the operating member cannot be sufficiently secured, and operability will be sacrificed.
In view of the above, it has been desired to develop an operating device which is designed so as to comply with the above described standard (2), without sacrificing the operability, while safety in an event of collision can be ensured.
FIGS. 1 and 2 show a conventional example of an operating device having such a structure as complying with the above described standard (2).
An operating device 1 herein disclosed is a volume switch which can be also used in an audio unit or the like mounted on a vehicle, and includes a switch member 3 having a shaft member 3a, and an operating member 5 having an engaging part 5a which has a substantially cylindrical shape and is adapted to be engaged with the shaft member 3a. 
The switch member 3 has a shaft holding part 3b which holds the shaft member 3a in a rotatable manner, and incorporates therein a volume circuit in which circuitry resistance is varied by the rotation of the shaft member 3a. Moreover, lead terminals 3c, which are connected to a circuit board 7 arranged inside an operating panel (not shown) of an audio unit or the like, are projected from the shaft holding part 3b. 
The operating member 5 includes a body part 5b having a headed tubular shape, which serves as a knob on occasion of rotational operation, and an engaging part 5a, which is uprightly provided at a center of an inner face of a head of the body part 5b, both of which are integrally formed of synthetic resin or the like.
An inner peripheral face of the engaging part 5a is spline-fitted to the shaft member 3a, and the rotation applied to the body part 5b becomes the rotation of the shaft member 3a as it is.
There are integrally provided ribs (steps) 6 on an inner periphery of the engaging part 5a, which are adapted to come into contact with a distal end of the shaft member 3a thereby to restrict an engaging depth of the shaft member 3a with respect to the engaging part 5a. 
These ribs 6 restrict the engaging depth of the shaft member 3a in such a manner that a gap 9 for allowing an axial displacement of the shaft member 3a is left at the distal end of the shaft member 3a, and thus, a protruding amount of the operating member 5 from the operating panel (not shown) can be secured.
Moreover, when a load F beyond a predetermined load in an axial direction of the shaft member 3a is applied to the operating member 5 by a collision or the like, these ribs 6 will be scraped off, and the distal end of the shaft member 3a will intrude into the gap 9. As the results, the operating member 5 will be pushed down to the operating panel by a depth corresponding to the gap 9. Accordingly, the protruding amount of the operating member 5 will be within the amount prescribed in the standard (2). Therefore, an injury of the passengers in the vehicle by a collision against the operating member 5 will be reduced (for example refer to JP-A-2002-184266).